The oldest spearthrower device to date was found in France to my understanding. Wiki says the ancient Greeks used leather slings to throw their javelins. And then there is little record of them being ever used again in Europe. I mean sure, bow and arrow are better for hunting large game, but that didn't stop the Mesoamericans from atlatls in warfare, even against the Europeans. It still seemed from there one that the Europeans still preferred to just throw javelins when they did use them, though that seems more for for sport than legitimate warfare. Is there something about having a cavalry that makes spear throwing impractical? Spears, pikes and halberds were useful against cavalry, but only when stationary. Could atlatls even be used from horseback?
Bows and crossbows allowed a soldier to carry more ammunition in a battle. As a general rule of thumb Javelin infantry carried roughly three (give or take one) javelins due to factors such as weight, the size of the javelins, and the cost. The amount of ammunition that archers carried also varied greatly, but were far more than Javelin-throwers. Some reports state that English Longbowmen carried 60 arrows, Byzantine archers carried about 40, and Arab archers carried about 30+. Likewise crossbowmen carried more bolts than Javelin throwers, with Genoese crossbowmen carrying about 20 or 25.